1. Field of the Invention
This invention relates to a blade type plug-in fuse for nominal currents in excess of or equal to 20 amperes, and more particularly to automobile blade type plug-in fuses.
2. Description of the Related Art
Blade type fuses are increasingly used in automobile equipment, for the purposes of space requirements, protective qualities and ease of plugging in. Such fuses generally comprise an insulating case or body in which is partially mounted a conductive unit constituted by two connection terminal blades joined together by a fuse link element or gauging part.
A fuse of this type is described in U.S. patent application Ser. No. 3,909,767.
However, the structure and type of materials used to manufacture these blade type plug-in fuses were chosen for a nominal current circulating in the fusible link element and connection terminal blades of less than 30 amperes.
For higher nominal currents of up to 100 amperes and more, the fuse link element can sag and come into contact with one of the inner sides of the insulating body or case. As the material used for the case is a plastic material, it ensues that the contact with the fuse link element is apt to melt the plastic material and to engender the complete deterioration of the case.
The sagging phenomenon generally occurs at the center of the gauging part since it is at this spot that the hottest point is situated when the temperature curve is plotted. The solutions that have been advocated to solve the sagging issue have either been to reduce the cross section of the gauging part in the region of the hot spot, or to deposit a drop of metal at the center of said gauging part when it is constituted by a metal wire, or to provide an opening in the region of the hot spot and deposit a drop of metal on both sides of the opening. All these solutions are disclosed in British patent application No. 2,090,081 and U.S. patent application Ser. No. 4,435,023. In the solution involving drops of tin deposited on both sides of the central opening, the structural parameters must be selected as a function of the nominal current of the flat fuse. In this way, the length, width and thickness of the fuse element are not the same for a 40-ampere flat fuse and for a 60-ampere flat fuse, which constitutes a serious drawback for large-scale production. Moreover, it may be necessary to change the location of the drops of tin and therefore of their openings where they are deposited as a function of the length of the fuse link element.
In German patent application No. 2,500,364, a flat fuse is described comprising a fuse link element produced in a single piece with the connection terminal blades, but which is partially recessed in the central part so as to produce a thinner zone of constant thickness and cross section, only the thinner zone constituting the gauging zone.
In the PCT/US88/02924 application, the gauging part of the fuse link element comprises cut-outs intended to provide cooling zones susceptible of generating a retarding effect on the sagging of said gauging part.